Try Tools-Options-Advanced and uncheck 'Use hardware acceleration when available'. Restart. I suggest this because you mentioned that Safe Mode fixes the issue, but disabling add-ons has no effect. Safe mode does both.

Let me know.

Thanks Smokva, Thunderbird doesn't have a disable hardware acceleration option but Firefox does so I disabled that - it didn't make a difference. (Firefox has always worked well) BTW I have seen mention of themes as a possible cause. I am using the default theme 34.0.5

Themes or other add-ons could definitely be a problem, but you mentioned that disabling all add-ons (which I assumed included the themes) made no difference. If that was an incorrect assumption, try disabling the themes and see what happens. However, there is a disable hardware accelerator option in Thunderbird. Tools-Options-Advanced and GENERAL tab (I forgot to specify that - my bad) and uncheck it. Do try that. I don't think doing it for Firefox would make any difference if the problem is with TB.

Thanks Smokva The TB theme is the default theme so it cannot be disabled. I do not use others. The version of TB I am using 31.4.0 does not have the disable hardware acceleration. I went through all the tabs.

Hmm.... you have an older version of TB. I'm pretty certain that all relatively recent TBs have the option to turn off hardware acceleration, they are just more difficult to find.

Here is a potential way to do so but in the mean time I'm going to try to touch base with someone that I also know has an older version and see if they can weigh in.

1. Go into TOOLS - OPTIONS - ADVANCED and click on 'Config Editor' button. It'll ask for confirmation, click on the "I'll be careful, I promise! button."

2. Now look for following 2 preferences:

   gfx.direct2d.disabled
   layers.acceleration.disabled

3. Both preferences would be set to false. Double-click on both of them and it'll change their values to true.

That's it. Restart the program and it'll turn hardware acceleration feature off.

I'm kind of focused on this potential solution because it does seem to support what you have described before - mainly that safe mode does fix the problem. So I really think this is worth trying out. However, if you are somewhat confused by what appears while following the above steps, just hold off and let me know. I'll try and confirm your version in the mean time.

As an aside, have you thought about upgrading to the current version?

Hi Smokva, Looks like it's fixed. Hurrah! As for upgrading TB - well... this is the third time that I have had a TB upgrade and then had a problem which takes weeks or months to sort out. So I think that I'll stick with this version for the time being but thanks for help! P

I'm glad the solution worked. And I completely understand your reluctance to upgrade right away. Let everyone else sort our the problems first. :) Just don't fall too far behind; obsolescence has its own problems as well.